One known solid oxide fuel cell system, as disclosed in our published European patent application EP0668622A1, comprises a solid oxide fuel cell stack and a gas turbine engine. The solid oxide fuel cell stack comprises a plurality of solid oxide fuel cells and each solid oxide fuel cell comprises an electrolyte, an anode and a cathode. The gas turbine engine comprises a compressor and a turbine arranged to drive the compressor. The compressor is arranged to supply oxidant to the cathodes of the solid oxide fuel cells and there are means to supply fuel to the anodes of the solid oxide fuel cells. A portion of the unused oxidant is supplied from the solid oxide fuel cells to the cathodes. A portion of the unused fuel is burnt in the remainder of the unused oxidant in a combustor and the products of the combustor drive the turbine. A heat exchanger may be provided to transfer heat from the products of the combustor to the oxidant supplied from the compressor to the at least one cathode to preheat the oxidant supplied by the compressor.
In this arrangement the combustor is arranged upstream of the high temperature heat exchanger.
A problem with this arrangement is that it is necessary to use a high temperature heat exchanger to transfer heat from the products of the combustor to the oxidant supplied from the compressor to the solid oxide fuel cells in order for the oxidant to reach the required temperature before entering the solid oxide fuel cell stack.